1. Field of the Invention
This invention relates to a hot chamber die casting machine for casting aluminum and its alloys, adapted to be employed where metallic injection systems cannot be used because of the erosive property of molten aluminum. Also, this invention relates more particularly to a hot chamber die casting machine using a ceramic injection system composed of four parts avoiding large one piece ceramic body and stress concentrations at critical points, and is made to be fixed to a structure outside of and independent from the molten metal holding container and the metal heating furnace.
2. Description of the Related Art
It is known that a hot chamber die casting process is more useful as compared with a cold chamber die casting process. Therefore, a hot chamber process has been widely used for casting zinc and magnesium alloys, with advantages in the quality of castings and the casting productivity. Particularly, in a hot chamber process, a molten metal goes into a die cavity without being cooled while it passes through the injection sleeve in contact with room temperature sleeve wall and also the molten metal does not pick up gas in contact with oily substance in the sleeve as in a cold chamber process.
Because molten aluminum and its alloys are substantially reactive and able to react with almost all metallic materials and erode them, until now, a hot chamber process using a cast iron injection system, as in the case of zinc and magnesium, could not be employed. Thus, only a cold chamber die casting machine has been used in die casting aluminum and its alloys, although many trials to utilize ceramic injection systems for casting aluminum and its alloys have been reported.
An injection system for molten aluminum and its alloys has to be made of ceramic and/or thermet materials. A conventional hot chamber die casting machine for casting aluminum alloys (such as that disclosed in Japanese Unexamined Utility Model Publication (Kokai) No. 5-57368) is shown in FIG. 15. In the conventional hot chamber die casting machine a furnace or base frame 6 with pot 4 for melting and accommodating molten metal 3 includes heaters 5 for heating the pot 4 to a certain temperature so as to keep the metal in the pot in a molten state. The pot 4, mounted on a base frame 6, is provided with an injection cylinder 1 and an injection pipe 13. The injection pipe 13 has a nozzle 44 which is forced and fastened to a mold 15 and 16 attached to a die-plate 52.
In order to rigidly connect the mold 15 and 16 to the nozzle 44, the base frame 6 is clamped to the die-plate 52 by a clamping means 53, the detailed explanation thereof being omitted. On the other hand, a plunger 12 is inserted in the injection cylinder 1 and the plunger 12 is connected to a hydraulically driven shaft 54 by means of a coupling 32, so that when a hydraulic cylinder moves the shaft 54 downward, the plunger 12 also moves downward to pressurize the molten metal in the injection cylinder 1. Thus, the molten metal flows through the injection pipe 13 and is injected via the nozzle 44 into the mold cavity 18 of the mold 15 and 16 and a casting operation is thus performed.
To secure the alignment of centers of the hydraulically driven shaft 54, the plunger 12 and the injection cylinder 1, the above mentioned conventional system has a fatal disadvantage. Because the injection cylinder 1 sits on the pot 4, the position of the injection cylinder 1 is not stable, since the pot 4 does not have a mechanically precise structure and also the dimension of the pot 4 changes due to a temperature change, for example, when the heater 5 is turned on, the pot 4 tends to expand resulting in a change of position of the injection cylinder 1. When this happens, normal functioning of the injection system is disturbed and the quality of the casting cannot be maintained. Therefore, with the above mentioned system, a frequent repositioning of the pot 4 is inevitable.
Japanese Unexamined Utility Model Publication (Kokai) No. 5-57368 (the present inventor is also one of the inventors of the U.M. registration) discloses a ceramic injection pipe separated from a ceramic injection cylinder and connected to the injection by means of a seal ring between flat surfaces. In this prior art, the seal ring must be compressed by a large axial force in order to seal the molten metal at the joint in a hot chamber die casting machine for aluminum. However, with this mechanism, a small fluctuation of the position of the nozzle part of injection pipe can deteriorate the sealing resulting in unstable operation.